(3) For tests requiring a certain speed for a certain
length of time, compute the time after the sample has
attained the desired speed.
(1) Check for gas bubbles in the lower mercury
(4) After loading the centrifuge, close both covers.
chamber or in the capillary column.
(5) Place the switch in the ON position and ad-just
(2) If bubbles are present or if the mercury in ;he
the large control knob to the desired reference point on
capillary column is broken, heat the bulb very carefully
until the bubbles are driven up into the expansion
chamber. Cool slowly in a vertical position, allowing the
mercury to pull back to form a solid column without
Never stop centrifuge by using
(3) If mercury is trapped in the head of the
hands. (6) To stop the centrifuge,
thermoregulator behind the adjusting collar, hold the
turn the large knob to full
thermoregulator at a slight angle with the head up.
counterclockwise position and place
Gently tap the head against the palm of the hand, while
switch in the OFF position.
rotating the unit. This will dislodge the mercury and allow
it to fall into the body of the thermoregulator, where it
2-16. Refrigerator Ice Maker.
must be joined to the mercury column.
. The laboratory refrigerator (fig. 2-9),
built into the front partition separating the laboratory
compartment from the utility compartment, is a complete
cabinet F1 (figs. 1-2 and B-12), is designed to comply
hermetically sealed condensing unit. The refrigerator is
with the requirements specified in ASTM Methods D91,
specifically designed as an ice cube producing and
D893, D1796, D2273, D2709, (TM 10-1166) and FTMS
storage unit. The unit has a freezing capacity of 16 ice
791, Method 5101.6. The centrifuge is installed so that
cube trays with an additional storage capacity of 23
its cover can be reached through a corresponding cover
in the counter top above the centrifuge at the left for-
ward end of the laboratory. A single-phase, 120-vac, 50
to 60 HZ, 2250 rpm motor, mounted within the base,
spins the head at speeds which are con-trolled by a
(1) Allow the unit to operate from 4 to 6 hours before
loading the interior with water-filled ice cube trays.
(2) When the ice cube trays are frozen, the cubes
can be stored in the stainless steel bin directly below the
shelves of the freezing compartment, or this space may
(1) Place samples in centrifuge so that the load is
be used for cooling quart samples.
balanced. The number of tubes and their respective
(3) If required, adjust the cold control for the proper
positions should be directly opposite one another. Tubes
are stored in drawer B1 (fig. B-8). If only one sample is
to be processed, another tube should be filled with a
liquid of the same weight and placed in position directly
across from the sample. If three samples are to be
(1) Remove power from the unit.
processed, they should be placed 90 degrees apart, and
(2) Open the door until accumulated ice has melted
a fourth tube with water should be placed in position to
and drained from the cabinet.
fulfill the quadrant.
(3) To accelerate melting, place several pans of hot
water in the freezing compartment.
(4) Wipe interior completely dry.
When inserting a centrifuge tube, be
(5) Supply power to the refrigerator and allow the
certain bottom of tube is in contact
unit to operate for at least 1 hour before replacing the
with padding. If it is not, insert
water-filled ice cube trays.
additional padding of felt or sponge
(2) The range of the centrifuge is up to 2000 rpm.
The calibrated reference dial allows the operator to
select the setting that will give the desired speed.